This invention relates to powder metallurgy and, more particularly, to methods for forging articles from powder steel alloys.
Powder forging is a process in which a porous preform produced by cold compaction and sintering is hot forged to reduce the pore content and increase strength. While over three decades old, powder forging still is an emerging technology. The growth of powder forging has been impeded by a number of factors including questions concerning the economic viability of the process, technical problems and process limitations. Pease, "An Assessment of Powder Metallurgy Today and Its Future Potentional", SAE Publication 831042 (1984). Despite these difficulties, powder forging has important advantages such as demonstrated capabilities in producing near-net or net shapes, excellent material and energy utilization and adaptability to automated production. Prior methods employing press forging are exemplified in U.S. Pat. Nos. 4,693,864 (Lloyd), 4,165,243 (Sarnes et al.), 4,002,471 (Sarnes et al.), 3,992,763 (Haynie et al.) and 3,837,068 (Dunn).
Currently, powder forging is carried out on forging presses, mainly mechanical and hydraulic presses. Use of impact forging, commonly applied to the conventional impression die forging of wrought steels, has a number of potentially important technical and economic advantages. One example is the ability of impact forging machines to achieve large forging forces at lost cost. This capability enables the use of large peak average forging pressures which favor the development of high densities and strengths in the forged part. Hendrickson et al., "Effect of Pressing Variables on the Mechanical Properties of P/M Forged and Heat Treated 4650-60 Steels", Horizons of Powder Met., Part 1 Proc. P/M, pp. 453-56 (1986). Despite these important advantages, impact forging has not been used for commercial powder forging.